1. Field
The present invention generally relates to a reception technology, and more particularly, to an FM receiver that receives an FM signal and method for receiving an FM signal.
2. Description of the Related Art
If an FM signal detected by an FM receiver is interfered by a buzz beat or the like, the quality of the signal is deteriorated. In order to deal therewith, in a television signal receiving circuit of intercarrier signal detection scheme, a buzz component included in an audio signal is canceled by adding a PM component that is quadrature-detected by an automatic frequency regulator circuit to an audio signal acquired by an audio detector circuit.
In an FM receiver comprising a quadrature detection device of direct conversion scheme or the like, a beat noise after the FM detection occurs. In order to reduce the effects thereof, a DC component of a FM detection signal (i.e., a frequency difference between a detected RF signal and a local oscillation signal) is detected for example by Automatic Frequency Control (AFC).
Further, by the detected frequency difference, the frequency of the local oscillator is adjusted so that the frequency is equal to the frequency of the detected RF signal. This reduces the frequency difference df, thus the frequency of beat noise is also reduced, and the beat noise becomes harder to hear as a sound.
Meanwhile, tone squelch, such as a Continuous Tone Coded Squelch System (CTCSS), a Digital-Coded Squelch (DCS), or the like is sometimes used for a walkie-talkie for business use. These tone squelches use a signal having a frequency lower than that of the audible band. Therefore, if the AFC described above is used for a tone squelch, since the AFC follows a signal for the tone squelch, the signal for the tone squelch after FM detection is attenuated and/or distorted. As a result thereof, the squelch malfunctions.